An electrostatic chuck is a device for adsorbing and fixing a wafer in a semiconductor manufacturing process, which is used in the process of deposition, etching, diffusion or the like.
An adsorption unit of an electrostatic chuck, which is a component for directly fixing a wafer in a plasma environment of a semiconductor manufacturing process, is mostly composed of a ceramic sheet or an insulating resin sheet having an anti-plasma characteristic. In addition, since the electrostatic chuck is an expensive device, it is generally reused after refurbishment to extend the lifespan, and, specifically, it is reproduced in a method of replacing the ceramic sheet or the insulating resin sheet of the adsorption unit with a new one.
In the case of a conventional electrostatic chuck, since an adhesive layer, which adheres the adsorption unit to a base substrate, is continuously exposed to plasma in a semiconductor manufacturing process, erosion occurs in the adhesive layer, and the adhesive layer is peeled off and it becomes a cause of particles in the process. And they result in wafer contamination and also the adsorbed wafer could be bent when a temperature difference occurs between the center and the periphery of the ceramic sheet or the insulating resin sheet of the adsorption unit.
As a prior art for preventing the conventional problem of separating an adhesive layer caused by plasma erosion on the adhesive layer and generating particles according thereto, a US patent entitled “Method And Apparatus For Repairing An Electrostatic Chuck Device, And The Electrostatic Chuck Device” (U.S. Pat. No. 8,252,132) has been publicized. The prior art prevents an adhesive layer from being exposed to plasma by winding a string-like adhesive around the adhesive layer formed between the base substrate and the adsorption unit using a bobbin device as shown in FIG. 1 of the patent specification.
However, since the prior art uses acrylic rubber and thermosetting resin, which are materials the same as those of the adhesive layer, as an adhesive, the adhesive is also not strong enough to have high resistance to the plasma and greatly affected by temperature, and, as a result, the prior art has a problem in that the adhesive is also separated by the plasma erosion and created as particles.
On the other hand, although a method of forming an erosion prevention coating layer by directly spraying ceramic powder on an exposed surface of the adhesive layer can be considered as a method for preventing the adhesive layer from being eroded in the plasma environment, it has problems described below.
First, when ceramic powder is sprayed on the exposed surface of the adhesive layer formed of resin for attaching the base substrate of the electrostatic chuck and the ceramic sheet using a thermal spraying method of spraying and coating ceramic powder by melting the ceramic powder at a temperature of 15,000K or higher or a cold spraying method of spraying and coating ceramic powder by heating the ceramic powder at a temperature of several hundred degrees Celsius, it is difficult to form a coating layer for protecting the adhesive layer since there is a problem of melting down the adhesive layer.
Second, although a chemical vapor deposition (CVD) method or a physical vapor deposition (PVD) method can be considered, since the two methods are appropriate for forming a thin film of 1 μm or less, it is difficult to apply the methods to forming a coating layer for protecting an exposed surface of the adhesive layer on the side surface of an electrostatic chuck placed in a plasma environment. Because a crack may occur in the coating layer if its thickness is 2 μm or above. In addition, although it is easy to form a coating layer on a plane using the coating methods, there is a disadvantage in that those coating methods have a difficulty in forming a coating layer uniformly on an exposed surface of an adhesive layer along the three-dimensional shape of the electrostatic chuck.
Third, there is another aerosol deposition (AD) method known as a method of spraying and coating ceramic powder in a vacuum state. Since by this method, spraying and coating the ceramic powder is possible at room temperature unlike the thermal spraying and cold spraying methods described above, the coating can be performed on the electrostatic chuck while the adhesive layer formed of resin is not melted. However, since the AD method uses a method of supplying aerosolized powder to a transfer tube which essentially needs an aerosol generator supplying and aerosolizing compressed gas and ceramic powder, like reference numeral 23 of FIG. 3 shown in the specification of U.S. Pat. No. 7,153,567 entitled “Composite Structure And Method And Apparatus For Forming The Same” (PCT/JP00/07076) and reference numeral 13 of FIG. 1 shown in the specification of U.S. Pat. No. 7,993,701 entitled “Composite Structure Forming Method”, it is disadvantageous in that a constant amount of scattered powder cannot be supplied to the transfer tube since the powder is irregularly scattered by the compressed gas, and it is difficult to make a coating film having a uniform thickness along the three-dimensional shape of curved surfaces, holes and protruded portions since the amount of powder cannot be controlled constantly.
In order to improve the disadvantage of the AD method incapable of providing a constant amount of powder to the transfer tube, an improved method of installing a constant supply mechanism of reference numeral 2 in the front stage of an aerosolation mechanism of reference numeral 4 of FIG. 16 of the specification, accommodating and aerosolizing prepared particles in an accommodation mechanism, and supplying the particles to a transfer tube has been proposed, as is described in the specification of U.S. Pat. No. 8,241,703 entitled “Pre-Formed Controlled Particle Formed Of Fine Particles Non-Chemically Bonded Together, Composite Structure Formation Method Involving Controlled Particles, And Composite Structure Formation System Involving Controlled Particle”. However, although a constant amount of powder is initially supplied from the accommodation mechanism containing the prepared particles and the constant supply mechanism themselves as shown in FIGS. 21 to 30 accompanied in the patent specification, the powder is supplied to the aerosol generator as shown in FIG. 16 of the specification in the same manner as shown in the U.S. Pat. Nos. 7,153,567 and 7,993,701, and the powder reaches a state of being transferred to the transfer tube irregularly and inconstantly in the end. That is, since the aerosol generator and the accommodation mechanism containing the powder are put into a vacuum state and the powder irregularly flows into the transfer tube when an AD coating apparatus operates, it is difficult to supply a constant amount of powder to the transfer tube.
On the other hand, the technique of U.S. Pat. No. 2008/0276865 entitled “Electrostatic Chuck, Manufacturing Method Thereof And Substrate Treating Apparatus” relates to a technique of forming a polycrystalline structure by spraying and coating yttria (Y2O3) powder on the adsorption surface (mounting surface) of an electrostatic chuck, which adsorbs and fixes a wafer, using the AD method. However, protrusions contacting with the bottom of the wafer exist on the adsorption surface of the electrostatic chuck, and the problem is that since the amount of powder supplied to the transfer tube from the aerosol generator cannot be constantly controlled by the nature of the system, thickness of the coating film on the protrusions and surrounding areas is non-uniform across the adsorption surface of the electrostatic chuck, and thus line patterns having a predetermined width are generated on the adsorption surface after AD coating is actually performed, and, therefore, it may negatively affect the electrical characteristics of the electrostatic chuck. Furthermore, due to the shape of the electrostatic chuck adsorbing a 200 or 300 mm wafer, it is difficult to form an erosion prevention coating layer on an exposed surface of the circular outer adhesive layer using the AD method. It is since that the powder is unevenly supplied to the transfer tube from the aerosol generator (aerosolation mechanism) by the nature of the system since this method is performed using an AD coating apparatus, and thus it is difficult to transfer a constant amount of powder to a spray nozzle. Accordingly, if coating is performed along the circular exposed adhesive layer, a phenomenon of separating the ceramic coating film from the exposed surface of the adhesive layer occurs, and thus the erosion prevention coating layer cannot be formed on the surface of the adhesive layer.
In conclusion, an adhesive layer erosion prevention coating layer capable of protecting an exposed surface of an adhesive layer, which adheres an adsorption unit adsorbing and fixing a wafer to a base substrate, from a plasma environment and not being peeled off from the exposed surface of the adhesive layer, is needed.